Occipital Bone Anatomy
Introduction to the Occipital bone anatomy:
- The occipital bone (L., occipital – “back of the head”) is a cranial bone that surrounds the back and base regions of the brain.
- Along with its inferior and internal surfaces is the prominent foramen magnum, which allows the spinal cord to pass through the skull.
- The broad, curved region superior to the foramen magnum is called the squamous part (= squama occipitalis) of the bone. Anterior to the foramen magnum is the basilar part and to the sides are the lateral parts.
Markings of the Occipital Bone:
- External occipital protuberance – elevation (larger in men) near the center of the squamous part; attachment point for ligamentum nuchae and trapezius muscle.[Posterior view/ Inferior view]
- Superior nuchal line – a ridge that runs horizontally from either side of the external occipital protuberance; attachment point for several muscles that control the position of the head and neck. [Posterior view/ Inferior view]
Quickly and easily learn the bones of the body with these interactive quizzes and labelling exercises.
- Highest nuchal line – a slight ridge above the superior nuchal line; attachment point for galea aponeurotica (connective tissue membrane that attaches the occipitalis and frontalis portions of occipitofrontalis muscle).[Posterior view]
- Median nuchal line – a slight vertical ridge that runs from external occipital protuberance to foramen magnum; attachment point for ligamentum nuchae. [Posterior view/ Inferior view]
- Inferior nuchal line – a ridge that runs horizontally from both sides of the median nuchal line below the superior nuchal line; attachment point for several muscles that control the position of the head and neck. [Posterior view/ Inferior view]
- Foramen magnum – large, oval opening at the base of the skull; passageway for spinal cord. [Inferior view/Superior View]
- Occipital condyle – prominent, rounded elevation located to the side of the foramen magnum; articulates with the superior articular facet of the atlas (1st) vertebra. [Inferior view]
- Jugular foramen – large, irregular opening along the junction of occipital and temporal bones; passageway for internal jugular vein and glossopharyngeal, vagus, and accessory nerves. [Inferior view/Superior View]
- Hypoglossal canal – hole located in basilar part of bone superior to occipital condyle; passageway for the hypoglossal nerve that controls movement of tongue. [Superior View]
- Internal occipital protuberance – elevation at the center of the cruciform eminence (= vertical and horizontal grooved ridges that divide internal surface of occipital bone into four fossa). [Superior View]
- Internal occipital crest – ridge that runs vertically from internal occipital protuberance to foramen magnum; attachment point for connective tissues (falx cerebelli) that anchors the brain. [Superior View]
- Groove (sulcus) for transverse sinus – indentations running horizontally from internal occipital protuberance; provide channels for transverse sinuses that drain venous blood from the brain to jugular foramen; also serve as attachment points for tentorium cerebelli (= dura mater that runs between the cerebellum and occipital lobes of the brain). [Superior View]
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Inferior view: [Show/Hide answers]
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The occipital bone (also known as C0) is a trapezoid skull bone that contributes to the posteroinferior part of the cranial vault. It is pierced by the foramen magnum, permitting communication from the cranial cavity to the vertebral canal.
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Occiput is a noun referring to the back of the head, it is not a synonym for the occipital bone. The occipital bone is also known as "C0" because it joins the skull to the first cervical vertebra or C1, forming the atlanto-occipital joint.
The occipital bone is composed of four parts:
- squamous part: external/internal surfaces
- basilar part (basiocciput): lower/upper surfaces
- lateral (jugular) parts (two): under/upper surfaces
The squamous part is the curved, expanded plate located behind the foramen magnum.
The external surface of the squamous part features:
- external occipital protuberance, the tip is known as the inion
- highest nuchal line
- superior nuchal line: occipitalis, trapezius, sternocleidomastoid, splenius capitis
- inferior nuchal line: rectus capitis posterior major and minor
- median nuchal line: attachment of ligamentum nuchae
- attachment of posterior atlanto-occipital membrane
The internal surface of the squamous part features:
- cruciate eminence divide region into four fossa; the upper two contain the occipital lobes while the lower two contain the cerebellar hemispheres
- internal occipital tuberosity at intersection
- sagittal sulcus for superior sagittal sinus, falx cerebri attaches to margins
- internal occipital crest gives attachment to falx cerebelli
- transverse grooves hold transverse sinuses
The basilar part is the quadrilateral piece in front of the foramen magnum.
The lower surface of the basilar part features:
- pharyngeal tubercle: attachment to fibrous raphe of pharynx
- either side of middle line: longus capitis, and rectus capitis anterior
- anterior atlanto-occipital membrane
The upper surface of the basilar part features:
The under surface of the lateral part features:
- occipital condyles: articulate with the atlas (C1), permitting flexion and extension (nodding) with minimal lateral flexion. No rotation occurs at the atlanto-occipital joint.
- the condyles are egg shaped and sloped inferomedially from anterior to posterior which helps limits mobility 2
- a third condyle may be a variant
- hypoglossal canal: at base of occipital condyles
- condylar fossa: behind condyle, receives posterior margin of superior facet of atlas, can be perforated by condyloid canal which contains an emissary vein from the transverse sinus
- jugular process, excavated in front by jugular notch, forming posterior part of jugular foramen
The upper surface of the lateral part features
The occipital bone articulates with 6 bones:
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The apical portion of the squamous part (above highest nuchal line): ossifies in membrane. Otherwise, the four parts ossify in cartilage.
Four parts are present at birth. Fusion occurs:
- 2nd year: squamous and jugulars
- 6th year: jugulars with basilar
- 25th year: basilar with basisphenoid
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Anatomy, Head and Neck, Occipital Bone, Artery, Vein, and Nerve
The occipital bone is the most posterior cranial bone and the main bone of the occiput. It is considered a flat bone, like all other cranial bones, meaning that its primary function is either for protection or to provide a broad surface for muscle attachment. The scalp, which consists of five layers, covers the bone. Going from superficial to deep, the scalp layers are skin, dense connective tissue, aponeurosis of the occipitofrontalis muscle, loose areolar connective tissue, and the periosteum. Within the dense connective tissue are the occipital artery and vein, and the lesser and greater occipital nerves. The inner part of the bone forms the posterior cranial fossa.
Structure and Function
The occipital bone is a very complex bone that serves primarily to protect the cerebellum and the occipital lobes of the cerebrum and to provide attachment to several muscles and ligaments described below. It is trapezoidal and shallowly curved on itself. It consists of outer and inner layers of cortical bone that sandwich cancellous bone, or diploe. It borders the parietal bones on either side superiorly to form the lambdoid suture, and the mastoid portion of the temporal bone to form the occipitomastoid suture on either side inferolaterally. The sphenoid bone articulates with it anteriorly via the inferior angle, and with the atlas inferiorly. The foramen magnum is part of the occipital bone, through which the medulla oblongata, the accessory nerves, the anterior and posterior spinal arteries, the vertebral arteries, the alar ligaments, and the tectorial membranes passes. It consists of three parts, including the basilar, condylar, and squamous parts, all of which have outer (facing the outside) and inner (facing the brain) parts.
The squamous part of the occipital bone is the most posterior and largest portion. It is the part of the bone that borders the parietal and temporal bone, and the posterior part of the foramen magnum. The outer squamous part contains several ridges or lines, crests, and prominences. There are three horizontal so-called nuchal lines. Superiorly to inferiorly, they are the supreme (also known as the highest), superior, and inferior nuchal lines. The supreme nuchal line begins about where the skull starts to curve inward to make the inferior surface and extends from midline to the lambdoid sutures on either side, curving slightly downward as it moves laterally. The superior nuchal line is larger than the supreme nuchal line, and it also extends from midline to the lambdoid sutures, curving slightly more than the supreme nuchal line laterally. At its midline is a prominence called the external occipital protuberance, with its highest point termed the inion. The superior nuchal line makes an intersection with a vertical midline ridge of bone called the medial nuchal line, which is also known as the external occipital crest, forming an uppercase “T” on the surface of the occipital bone. The superior nuchal line provides an attachment surface on its inferomedial side for the semispinalis capitis muscle, and on its inferolateral side for the obliquus capitis superior. The medial nuchal line extends caudally in a straight line to the foramen magnum, and with the inion, serves as the attachment for the nuchal ligament and the trapezius muscle. The inferior nuchal line transects the medial nuchal line approximately at its midpoint, curving more downward than the supreme or superior nuchal lines.
The cranial, or inner surface of the occipital bone makes up the base of the posterior cranial fossa. On the squamous part of the inner surface is a midline vertical ridge called the median internal occipital crest that runs from a median prominence called the internal occipital protuberance to the foramen magnum. The median internal occipital crest provides attachment for the falx cerebri and contains a groove for the occipital sinus. Running from the internal occipital protuberance to the superior border is the groove for the superior sagittal sinus. On each side of the internal occipital protuberance is a groove for the transverse sinus. The meeting point of the superior sagittal sinus, the straight sinus, and the occipital sinus is called the confluence of the sinuses, which drains the venous blood into the right and left transverse sinuses. These internal structures form a lower case “t”: the top of the “t” is comprised of the superior sagittal sinus groove, the intersection of the lines making the “t” is the internal occipital protuberance, the horizontal line of the “t” are the grooves for the transverse sinus, and the lower part of the “t” is the median internal occipital crest. This lower case “t” is also known as the cruciform eminence, due to its cross, or crucifix-like structure. Therefore, this structure divides the concave internal surface of the occipital bone to make four distinct fossae: two upper fossae, and two lower fossae. The upper fossae are called the cerebral fossa and hold the occipital lobes of the cerebrum. The lower fossae are called the cerebellar fossae and hold the hemispheres of the cerebellum. The inferior edge of the squamous part of the inner occipital bone makes up the posterior part of the foramen magnum. It contains a landmark called the opisthion, the midpoint of the posterior margin of the foramen magnum. It has a twin at the midpoint of the most anterior margin of the foramen magnum called the basion, located on the basilar part of the occipital bone, that lines up with the dens of the atlas.
The condylar part makes up the lateral edges of the foramen magnum on the undersurface of the occipital bone and is also known as the exoccipitals. It is made up of protuberances on either side of the foramen magnum called the occipital condyles, serving as an articular surface to the superior facets of the atlas. At the base of the condyles on the cranial (inner) side is the hypoglossal canal where the hypoglossal nerve exits, and a branch of the ascending pharyngeal artery enters. Posterior to the condyles is the condyloid fossa, a depression that articulates with the superior facet of the atlas during neck extension. Within the fossa is the condylar canal, where there may be an occipital emissary vein that perforates the bone to connect the occipital sinus, sigmoid sinus, and suboccipital venous plexus. The capsules of the atlantooccipital articulation attach to the margins, and medial to these is a tubercle where the alar ligament attaches. The jugular process comprises the anterolateral part of the bone on either side, on which the rectus capitis lateralis muscle inserts. Anterior to these processes is the jugular notch, forming the posterior portion of the jugular foramen.
The inner surface of the condylar part makes up the sides of the foramen magnum and contains the hypoglossal canals, as previously mentioned. More lateral to the hypoglossal canal is the jugular foramen, located at the junction of the occipital bone and the petrous portion of the temporal bone.
The basilar part makes up the anterior portion of the foramen magnum on the undersurface of the occipital bone and connects to the sphenoid bone. It is thick and quadrilateral in shape. The anterior atlantooccipital membrane attaches to its inferior surface immediately anterior to the foramen magnum. Even more anterior to the foramen magnum is the pharyngeal tubercle, the attachment site of the fibrous raphe of the pharynx. On either side of the midline of its inferior surface, the basilar part provides muscular attachment of the longus capitis and rectus capitis anterior muscles. The upper surface of the basilar part supports the medulla oblongata with its broad, shallow groove called the clivus, where the abducens nerve also runs nearby. It also provides attachment to the tectorial membrane near the foramen magnum. The lateral surface of the basilar part forms a junction with the petrous portion of the temporal bone to form the inferior petrosal sulcus, in which the inferior petrosal sinus lies. The inferior petrosal sinus receives veins from the medulla, pons, the inferior surface of the cerebellum, and the internal auditory veins and drains into the internal jugular vein. The inner basilar part contains the basion, as previously mentioned.
The occipital bone, like all other bones of the skull, develops from neural crest cells and paraxial mesoderm. It develops through both intramembranous and endochondral ossification. Intramembranous ossification refers to connective tissue membrane replacement with bony tissue, whereas endochondral ossification refers to the replacement of hyaline cartilage with bony tissue. The occipital plane, part of the squamous occipital bone, develops via the former model, and the remainder of the occipital bone forms via endochondral ossification.
There are typically four nuclei in the occipital plane to develop via intramembranous ossification. The nuchal plane of the squamous occipital bone ossifies via endochondral ossification from two nuclei. Occasionally, a Kerckring center will form at the posterior margin of the foramen magnum that will go on to form a separate ossicle. The condylar occipital bone ossifies from two centers, one center for either side of the foramen magnum, and the basilar part ossifies from two centers as well. Ossification of the occipital bone may occur as early as the ninth week of gestation. There had been much debate regarding the development and ossification process in the past, but recent studies of the complex gene and molecule interactions involved have helped with clarification.
Blood Supply and Lymphatics
The occipital area receives its blood supply from the occipital artery, and the blood drains via the occipital vein. The occipital artery has its origin from the external carotid artery, where it is deep to the digastric posterior belly and the hypoglossal nerve winds around it. It travels superiorly and posteriorly, passing superficially to the internal carotid artery and the vagus nerve, before anastomosing with the deep cervical artery as it courses just beneath the mastoid process of the temporal bone. It then travels along the deep to the sternocleidomastoid and splenius capitis muscles until it reaches the occipital bone's superior nuchal line, where it then travels superficially to the semispinalis capitis muscle. After it has coursed about halfway across the semispinalis capitis and just lateral of the trapezius, the artery then courses vertically up the back of the head superficial to the occipital belly of the occipitofrontalis. It ascends tortuously up the head in the superficial fascia, anastomosing with a branch of the posterior auricular artery. Then at the crown of the head, it anastomoses with the parietal branch of the superficial temporal artery.
The occipital artery supplies blood to more than just the occipital area, as evidenced by its several branches, including the auricular, descending, meningeal, muscular, and sternocleidomastoid branches. The auricular branch supplies the area behind the ear, and a mastoid branch supplies the mastoid air cells, diploe, and dura mater. The descending branch is the largest division and contains a deep and superficial portion. The superficial portion provides blood to the trapezius, and the deep portion anastomoses with a branch of the costocervical trunk, providing collateral circulation via the external carotid and the subclavian artery. The meningeal branch supplies the posterior cranial fossa dura mater. The muscular branches supply several muscles along the course of the occipital artery, including the digastric and longus capitis muscles. The sternocleidomastoid branch divides at the carotid triangle into upper and lower branches and supplies the muscle it is named after.
The occipital vein originates from small vessels on the posterior aspect of the scalp and drains the superficial muscles and skin of the occipital region. It is superficial to the occipital fascia and the occipital artery and anastomoses laterally with the parietal branch of the superficial temporal vein and inferolateral to the posterior auricular vein. It then runs into the inferior portion of the posterior auricular vein, where it becomes the external jugular vein. The occipital vein also has an anastomosis with the intracranial confluence of the sinuses via the occipital emissary vein. The occipital lymph nodes are located posterior to the occipital artery and vein, with the occipital lymph vessels draining into the jugulodigastric lymph node, which then drains into the jugular lymph vessels.
Sandwiching the occipital artery and vein is the lesser occipital nerve branch anteriorly and the greater occipital nerve branch posteriorly. The lesser occipital nerve, as well as the greater occipital nerve, branches off of spinal nerve C2 just as it passes directly inferior to the first cervical vertebra, carrying fibers originating from the ventral primary ramus. It supplies cutaneous innervation to the surface of the auricle posteriorly, as well as the adjacent posterior portion of the scalp.
In contrast to the lesser occipital nerve, the greater occipital nerve carries fibers from the dorsal primary ramus of spinal nerve C2, specifically its medial branch. It innervates the skin of the posterior scalp and the muscles of the posterior neck, the multifidus cervicis muscle, and the semispinalis capitis muscle. It also contains pain and proprioceptive branches for the suboccipital muscles and meningeal branches to the posterior cranial fossa.
The posterior auricular nerve innervates the occipital belly of the occipitofrontalis muscle that covers much of the surface area of the occipital bone.
As mentioned above, the occipital bone contains the foramen magnum, through which the spinal cord and accessory spinal nerve travel along with several blood vessels.
The occipital belly of the occipitofrontalis covers much of the occipital bone. This muscle helps move the scalp, elevate the eyebrow, and wrinkle the forehead skin. Its origin is from the lateral two-thirds of the supreme nuchal line of the occipital bone (as well as the mastoid process of the temporal bone) and inserts at the epicranial aponeurosis. The occipital artery and vein supply blood flow and drainage, and the occipital lymph nodes and vessels drain lymph. The posterior auricular nerve innervates it; the facial nerve innervates the remainder of the occipitofrontalis.
Several muscles attach to the inferior part of the occipital bone, whose insertions were discussed in the “Structure and Function” section. The most medial and superficial of these is the trapezius, with its multiple origins, one of which is the external occipital protuberance. Its innervation and blood supply will not be discussed here.
Just deep and on either side of the vertebrae are the left and right semispinalis capitis muscles, serving to extend and flex the cervical and thoracic spine and head laterally. These muscles are innervated by the dorsal primary rami of spinal nerves C3 to T6 and receive blood from the posterior intercostal arteries, the deep cervical artery, and the lumbar arteries.
Deeper still are the left and right rectus capitis posterior minor muscles, which help extend the head. Lateral of the rectus capitis posterior minor muscles are the rectus capitis major muscles, which help with ipsilateral rotation and head extension. Lateral and superficial to the major rectus capitis is the obliquus capitis superior muscle, which serves the same function as the former. The rectus capitis posterior minor, posterior major, and obliquus superior muscles are all innervated by the suboccipital nerve and blood supplied by the occipital artery.
The most lateral muscle of the occipital bone is the rectus capitis lateralis, serving to flex the head laterally. This muscle receives innervation from the spinal nerves C1 to C2 and receives arterial supply via the deep cervical artery. The longus capitis and the rectus capitis anterior muscles are anterolateral and anteromedial muscles of the occipital bone, whose function is to flex the head and neck.
The cervical plexus innervates the longus capitis, and the ventral primary rami of the spinal nerves C1 to C4 and receive arterial flow from the deep cervical artery. The rectus capitis anterior receives its nerve supply from the ventral primary rami of the spinal nerves C1 and receives arterial flow from the ascending cervical artery.
The occipital emissary vein may not be present in all individuals, and it may only pass through a singular condylar canal, or through multiple, smaller clustered canals.
The jugular tubercle on the upper surface of the lateral condylar part of occipital bone may sometimes have an oblique groove for cranial nerves IX, X, and XI.
The occipital artery may sometimes branch to give the mastoid artery; most of the time, this artery arises from the auricular branch of the occipital artery.
Cerebral dural sinus venous blood flow in the torcular Herophili, also known as the confluence of the sinuses, on occipital bone’s inner surface is variable. It categorizes into four types based on the continuity between the transverse sinus grooves and the superior sagittal sinus grooves. In descending order of frequency, these types are the right dominant type, confluence type, bifurcation type, and left dominant type.
See lacerations below in clinical significance.
Deep lacerations to the occiput and scalp, in general, are inclined to bleed profusely for several reasons:
The firm adherence of the dense connective tissue to the blood vessels prevents vasoconstriction.
The pulling effect of the occipitofrontalis muscle prevents the closing of the actively bleeding vessel and the surrounding skin.
There are numerous anastomoses of the scalp blood vessels, such as the anastomosis of the occipital and the posterior auricular veins.
The scalp veins may be used for venous catheterization as they offer easy access with little risk, with the occipital vein being among the most commonly used. Scalp catheterization is utilized in infants and neonates after unsuccessful attempts at cannulation of extremity veins as the scalp veins in this population have less overlying subcutaneous fat and are more prominent compared to other peripheral sites, and they are less obscured by hair, providing easier visualization and cannulation.
The ‘danger area of the scalp’ refers to the layer of loose areolar connective tissue as it contains the valveless emissary veins that connect the superficial veins in the subaponeurotic space with the intracranial venous sinuses. Although not always present, the occipital emissary vein connects the occipital vein to the confluence of the sinuses. This connection makes it possible for an infection to spread from the occipital scalp to the meninges.
Since the abducens nerve runs near the clivus of the basilar part of the occipital bone, increased intracranial pressure may trap the nerve at this point, causing abducens palsy. The clivus also serves as a critical landmark for ensuring anatomical atlanto-occipital alignment on cervical spine x-rays.
Occipital trauma may cause a basilar skull fracture, which would present with ecchymosis behind the ears, or “battle sign.” If occipital bone surrounding the foramen magnum is fractured, there is a higher risk of damage to the exiting blood vessels and nerves described above.
During delivery, it is crucial to identify the location of the fetal occiput. Several genetic disorders may present with a prominent occiput, the most common of which is trisomy 18, or Edwards syndrome. This condition is important to identify because of its association with heart (most commonly VSDs and ASDs) and renal defects, among others, and survival beyond one year of life is rare, although many of the afflicted will not make it to birth. Other signs that would be indicative of Trisomy 18 are microcephaly, micrognathia, low-set and malformed ears, and rocker bottom feet. It is associated with omphalocele.
Scalp Nerves and Arteries, Supratrochlear nerve, Supraorbital nerve, Zygomaticotemporal nerve, Auriculotemporal nerve, Lesser occipital nerve, Greater occipital nerve, Supratrochlear artery, Supratorbital artery, Zygomaticotemporal artery, Superficial (more...)
The Posterior Divisions, Posterior primary divisions of the upper three cervical nerves, Great Occipital Nerve. Contributed by Gray's Anatomy Plates
Cranial Bones, Occipital bone; Outer surface Foramen Magnum, Highest nuchal line, Hypoglossal canal. Contributed by Gray's Anatomy Plates
Suboccipital and Back Muscles, posterior view. Henry Gray (1918). Anatomy of the Human Body. Revised by Warren H. Lewis. Public domain.
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The occipital bone (Latin: os occipitale) is a single bone and consists of four parts that surround the foramen magnum.
Parts of occipital bone
There four parts forming the occipital bone are as following:
- Basilar part
- Lateral part (2)
- Squamous part
Basilar part of occipital bone
The basilar part of the occipital bone (also called the basioccipital) is the portion of the occipital bone extending anteriorly from the foramen magnum and joining with the body of the sphenoid bone.
The basilar part of the occipital bone has an internal and an external surface.
The internal surface of the basioccipital features the following structures:
- Groove for inferior petrosal sinus (2)
The clivus is a sloping medial surface of the basal part of the occipital bone behind the dorsum sellae, sloping downward to the foramen magnum. The clivus is occupied by the medulla oblongata and pons.
The groove for inferior petrosal sinus is formed by the junction of the petrous part of the temporal bone with the basilar part of the occipital bone.
The external surface of the basioccipital features the pharyngeal tubercle.
The pharyngeal tubercle (or pharyngeal eminence) is a prominence on the inferior surface of the occipital bone, specifically, on the outer surface of the basilar part of the occipital bone, for attachment of the pharyngeal raphe.
Lateral part of occipital bone
Each lateral part of the occipital bone has an internal and an external surface.
The internal surface of the lateral part of the occipital bone presents the groove for the sigmoid sinus.
The groove for the sigmoid sinus is located in the posterior cranial fossa, found on the lateral part of the occipital bone, then curving around the jugular process on the mastoid part of the temporal bone, finally, turning sharply on the inner surface of the parietal bone, continuing as the transverse groove.
The external surface of the lateral part of the occipital bone features the following structures:
- occipital condyle,
- condylar canal,
- hypoglossal canal.
The occipital condyle is a process on the occipital bone for articulation with the atlas.
The condylar canal is a bony passage located in the lateral part of the occipital bone posterior to the occipital condyle transmitting a vein from the sigmoid sinus.
The hypoglossal canal is a bony passage that originates from the lateral part of the occipital bone anterior to the foramen magnum and ends on the outer surface anterior to the occipital condyle. The hypoglossal canal transmits the hypoglossal nerve (CN XII) and a venous plexus.
Squamous part of occipital bone
The squamous part (also called squama of occipital bone, occipital squama) of the occipital bone has an internal and an external surface.
The internal surface of the squama of the occipital bone features:
- Internal occipital protuberance
- Internal occipital crest
- Groove for superior sagittal sinus
- Groove for transverse sinus (2)
The internal occipital protuberance is a prominent midpoint of the cruciform eminence - a cross shaped bony prominence on the internal surface of the occipital bone.
The internal occipital crest is a thick bony ridge on the internal surface of the occipital bone that occasionally extends from the internal occipital protuberance to the foramen magnum.
The groove for the superior sagittal sinus is a shallow depression on the frontal, parietal, and occipital bones forming a channel for the sagittal superior sinus; its margins come together as it passes downward and become continuous with the frontal crest.
The groove for the transverse sinus is located bilaterally on the internal surface of the occipital bone extending from the internal protuberance to the lateral angles of the occipital bone.
The external surface of the squama of the occipital bone features:
- external occipital protuberance,
- external occipital crest,
- superior nuchal line,
- inferior nuchal line.
The external occipital protuberance is a palpable bony projection in the middle of the occipital bone.
The external occipital crest is a bony ridge on the external surface of the occipital bone that occasionally extends from the external occipital protuberance to the foramen magnum.
The superior nuchal line is a transverse ridge on the external surface of the occipital bone at the level of the external occipital protuberance. It is the attachment site for the occipital belly of the occipitofrontalis muscle.
The inferior nuchal line is a transverse ridge on the external surface of the occipital bone between the superior nuchal line and the foramen magnum. The semispinalis capitis muscle attaches between the inferior and the superior nuchal lines.
Bone basilar occipital
Basilar part of occipital bone
Section of the main skull bone that extends forward and upward
The basilar part of the occipital bone (also basioccipital) extends forward and upward from the foramen magnum, and presents in front an area more or less quadrilateral in outline.
In the young skull this area is rough and uneven, and is joined to the body of the sphenoid by a plate of cartilage.
By the twenty-fifth year this cartilaginous plate is ossified, and the occipital and sphenoid form a continuous bone.
On its lower surface, about 1 cm. in front of the foramen magnum, is the pharyngeal tubercle which gives attachment to the fibrous raphe of the pharynx.
On either side of the middle line the longus capitis and rectus capitis anterior are inserted, and immediately in front of the foramen magnum the anterior atlantooccipital membrane is attached.
The upper surface, which constitutes the lower half of the clivus, presents a broad, shallow groove which inclines upward and forward from the foramen magnum; it supports the medulla oblongata, and near the margin of the foramen magnum gives attachment to the tectorial membrane
On the lateral margins of this surface are faint grooves for the inferior petrosal sinuses.
Human skull seen from below. Basilar part shown in red.
Human skull seen from above (parietal bones have been removed). Basilar part shown in red.
Occipital bone. Outer surface.
Membrana tectoria, transverse, and alar ligaments.
The anterior vertebral muscles.
Basilar part of occipital bone
Basilar part of occipital bone
Basilar part of occipital bone
Tympanic cavity. Facial canal. Internal carotid artery.
This article incorporates text in the public domain from page 132 of the 20th edition ofGray's Anatomy(1918)
Saucer-shaped membrane bone situated at the back and lower part of the cranium
The occipital bone () is a cranialdermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occipital lobes of the cerebrum. At the base of skull in the occipital bone, there is a large oval opening called the foramen magnum, which allows the passage of the spinal cord.
Like the other cranial bones, it is classed as a flat bone. Due to its many attachments and features, the occipital bone is described in terms of separate parts. From its front to the back is the basilar part, also called the basioccipital, at the sides of the foramen magnum are the lateral parts, also called the exoccipitals, and the back is named as the squamous part. The basilar part is a thick, somewhat quadrilateral piece in front of the foramen magnum and directed towards the pharynx. The squamous part is the curved, expanded plate behind the foramen magnum and is the largest part of the occipital bone.
Due to its embryonic derivation from paraxial mesoderm (as opposed to neural crest, from which many other craniofacial bones are derived), it has been posited that "the occipital bone as a whole could be considered as a giant vertebra enlarged to support the brain."[page needed]
The occipital bone, like the other seven cranial bones, has outer and inner layers (also called plates or tables) of cortical bone tissue between which is the cancellous bone tissue known in the cranial bones as diploë. The bone is especially thick at the ridges, protuberances, condyles, and anterior part of the basilar part; in the inferior cerebellar fossae it is thin, semitransparent, and without diploë.
Near the middle of the outer surface of the squamous part of the occipital (the largest part) there is a prominence – the external occipital protuberance. The highest point of this is called the inion.
From the inion, along the midline of the squamous part until the foramen magnum, runs a ridge – the external occipital crest (also called the medial nuchal line) and this gives attachment to the nuchal ligament.
Running across the outside of the occipital bone are three curved lines and one line (the medial line) that runs down to the foramen magnum. These are known as the nuchal lines which give attachment to various ligaments and muscles. They are named as the highest, superior and inferior nuchal lines. The inferior nuchal line runs across the midpoint of the median nuchal line. The area above the highest nuchal line is termed the occipital plane and the area below this line is termed the nuchal plane.
The inner surface of the occipital bone forms the base of the posterior cranial fossa. The foramen magnum is a large hole situated in the middle, with the clivus, a smooth part of the occipital bone travelling upwards in front of it. The median internal occipital crest travels behind it to the internal occipital protuberance, and serves as a point of attachment to the falx cerebri.
To the sides of the foramen sitting at the junction between the lateral and base of the occipital bone are the hypoglossal canals. Further out, at each junction between the occipital and petrous portion of the temporal bone lies a jugular foramen.
The inner surface of the occipital bone is marked by dividing lines as shallow ridges, that form four fossae or depressions. The lines are called the cruciform (cross-shaped) eminence.
At the midpoint where the lines intersect a raised part is formed called the internal occipital protuberance. From each side of this eminence runs a groove for the transverse sinuses.
There are two midline skull landmarks at the foramen magnum. The basion is the most anterior point of the opening and the opisthion is the point on the opposite posterior part. The basion lines up with the dens.
See also: Foramen magnum
The foramen magnum (Latin: large hole) is a large oval foramen longest front to back; it is wider behind than in front where it is encroached upon by the occipital condyles. The clivus, a smooth bony section, travels upwards on the front surface of the foramen, and the median internal occipital crest travels behind it.
Through the foramen passes the medulla oblongata and its membranes, the accessory nerves, the vertebral arteries, the anterior and posterior spinal arteries, and the tectorial membrane and alar ligaments.
The superior angle of the occipital bone articulates with the occipital angles of the parietal bones and, in the fetal skull, corresponds in position with the posterior fontanelle.
The lateral angles are situated at the extremities of the groove for the transverse sinuses: each is received into the interval between the mastoid angle of the parietal bone, and the mastoid portion of the temporal bone.
The inferior angle is fused with the body of the sphenoid bone.
The superior borders extend from the superior to the lateral angles: they are deeply serrated for articulation with the occipital borders of the parietals, and form by this union the lambdoidal suture.
The inferior borders extend from the lateral angles to the inferior angle; the upper half of each articulates with the mastoid portion of the corresponding temporal, the lower half with the petrous part of the same bone.
These two portions of the inferior border are separated from one another by the jugular process, the notch on the anterior surface of which forms the posterior part of the jugular foramen.
The lambdoid suture joins the occipital bone to the parietal bones.
The occipitomastoid suture joins the occipital bone and mastoid portion of the temporal bone.
The sphenobasilar suture joins the basilar part of the occipital bone and the back of the sphenoid bone body .
The petrous-basilar suture joins the side edge of the basilar part of the occipital bone to the petrous-part of the temporal bone .
The occipital plane [Fig. 3] of the squamous part of the occipital bone is developed in membrane, and may remain separate throughout life when it constitutes the interparietal bone; the rest of the bone is developed in cartilage.
The number of nuclei for the occipital plane is usually given as four, two appearing near the middle line about the second month, and two some little distance from the middle line about the third month of fetal life.
The nuchal plane of the squamous part is ossified from two centers, which appear about the seventh week of fetal life and soon unite to form a single piece.
Union of the upper and lower portions of the squamous part takes place in the third month of fetal life.
An occasional centre (Kerckring) appears in the posterior margin of the foramen magnum during the fifth month; this forms a separate ossicle (sometimes double) which unites with the rest of the squamous part before birth.
Each of the lateral parts begins to ossify from a single center during the eighth week of fetal life. The basilar portion is ossified from two centers, one in front of the other; these appear about the sixth week of fetal life and rapidly coalesce.
The occipital plane is said to be ossified from two centers and the basilar portion from one.
About the fourth year the squamous part and the two lateral parts unite, and by about the sixth year the bone consists of a single piece. Between the 18th and 25th years the occipital and sphenoid bone become united, forming a single bone.
Trauma to the occiput can cause a fracture of the base of the skull, called a basilar skull fracture. The basion-dens line as seen on a radiograph is the distance between the basion and the top of the dens, used in the diagnosis of dissociation injuries.
Genetic disorders can cause a prominent occiput as found in Edwards syndrome, and Beckwith–Wiedemann syndrome.
The identification of the location of the fetal occiput is important in delivery.
Occipital : from Latin occiput "back of the skull", from ob "against, behind" + caput "head". Distinguished from sinciput (anterior part of the skull).
In many animals these parts stay separate throughout life; for example, in the dog as four parts: squamous part (supraoccipital); lateral parts–left and right parts (exoccipital); basilar part (basioccipital).
The occipital bone is part of the endocranium, the most basal portion of the skull. In Chondrichthyes and Agnatha, the occipital does not form as a separate element, but remains part of the chondrocranium throughout life. In most higher vertebrates, the foramen magnum is surrounded by a ring of four bones.
The basioccipital lies in front of the opening, the two exoccipital condyles lie to either side, and the larger supraoccipital lies to the posterior, and forms at least part of the rear of the cranium. In many bony fish and amphibians, the supraoccipital is never ossified, and remains as cartilage throughout life. In primitive forms the basioccipital and exoccipitals somewhat resemble the centrum and neural arches of a vertebra, and form in a similar manner in the embryo. Together, these latter bones usually form a single concave circular condyle for the articulation of the first vertebra.
In mammals, however, the condyle has divided in two, a pattern otherwise seen only in a few amphibians.
Most mammals also have a single fused occipital bone, formed from the four separate elements around the foramen magnum, along with the paired postparietal bones that form the rear of the cranial roof in other vertebrates.
Position of occipital bone (shown in green). Animation.
Median sagittal section through the occipital bone and first three cervical vertebræ.
This article uses anatomical terminology.
This article incorporates text in the public domain from page 129 of the 20th edition ofGray's Anatomy(1918)
- Susan Standring; Neil R. Borley; et al., eds. (2008). Gray's anatomy: the anatomical basis of clinical practice (40th ed.). London: Churchill Livingstone. ISBN .
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